JPS60131820A - Manufacture of silicon carbide or mixture containing silicon carbide - Google Patents

Abstract

PURPOSE:To manufacture silicon carbide economically by a reducing method without using electric heating energy by using a specific vertical combustion furnace capable of heating a refractory tube in which raw materials are flowed downward, in a long range of the pipe at a prescribed temperature. CONSTITUTION:Plural long-sized refractory tubes 5 are provided vertically in the inside of a combustion chamber 4 of vertical furnace and, on the other hand, many blowing inlets 13 of oxygen (or air) are provided to the furnace refractories 7 of the side wall in the upper and lower directions. Gaseous fuel (for example, gas consisting essentially of H2 and CO) blowing in from an introducing inlet 15 is burned stepwise with oxygen blowing in from an introducing inlet 17 and a high temperature part of 1,650-2,000 deg.C is formed along the refractory tubes 5 in the long range. By using the furnace, briquettes consisting of silicon compound and carbon in prescribed ratios are charged to the inside of the refractory tubes 5 from a hopper 1 and are caused to fall down while forming the transferring packed bed and these are heated intermediately and caused to react for the period and the produced silicon carbide is taken out from the outlet of a hopper 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing silicon carbide mainly using combustion heat of gaseous fuel.

[Technical background of the invention and its problems]

Conventionally, most silicon carbide has been produced in an Acheson furnace, which is an electric resistance heating furnace, and is mainly crystalline α-type silicon carbide. This is used in abrasive materials and refractory materials, etc.
It has certain desirable properties. On the other hand, β-type silicon carbide has been the subject of recent research, but it seems that no inexpensive manufacturing method has been established. -For example, JP-A-52-46
There is a method described in No. 399. Although this method is not explicitly stated, the text clearly assumes electrical heating.
There seems to be a constraint on input energy. Since the present invention is a relatively low-temperature reduction method (although it is a method for producing silicon carbide), β-type silicon carbide is obtained as a result, but it is not possible to reduce The use of this method is rarely determined by its crystal type, so it will not be specified as a production method for the β type.

Due to the recent rise in energy prices, energy input has been reduced in all industries.In particular, in the case of silicon carbide, all of its production uses electrical energy, and according to the literature, it is generally said that the amount of energy input is reduced using the heat of combustion of fuel. are extremely rare. However, silicon carbide can be obtained by heating a mixture of silicic anhydride and carbon.
It is well known that it begins to form at the Ooc position and transforms into silicon carbide at a sufficient rate at temperatures above 1500°C. Therefore, economical manufacturing methods and equipment were not known.
Scarcity. From this perspective, the present inventor has conducted research into producing silicon and silicon carbide using the combustion heat of fuel.

Now, the major uses of silicon carbide are refractories and abrasive materials.
It is used as a reducing agent and heat generating material in iron and steel smelting and iron casting. In addition, it is known that ferroalloys containing a large amount of silicon, such as ferrosilicon, silicomanganese, and silinichrome, are formed intermediately in the electric furnace production of silicon, and conversely, they are carbonized during the production process. It is also known that smelting power can be reduced by adding silicon to the raw materials. However, the amount used for such purposes is extremely small. This is because conventionally, silicon carbide has no expensive, high-quality manufacturing method for use in high-grade applications such as abrasives.

[Structure of the invention]

In the present invention, silica stone (StO□) and reducing carbon raw material (C) are mixed in the form of fine particles or powder in a ratio of about 1 mol to 3 mol so as to produce silicon carbide (StC) through a reduction reaction. The briquette is obtained and charged into a highly heat-resistant refractory pipe to form a moving packed bed. A large number of these refractory pipes are set up in a heating furnace, and gaseous fuel is supplied from the lower part of the heating furnace. The idea is to introduce silicon carbide and burn it in multiple stages to form a wide high temperature range to produce silicon carbide.

As mentioned above, the conditions for the formation of silicon carbide are clear, but
The inventor tried this again. Grinding silica stone to 100 mesh or less, ■ Crushed petroleum coke to 200 mesh or less,
Mixed at a weight ratio of 1:0.61, asphalt 5
Add 5% of asphalt emulsion consisting of 0% and 50 parts of water to the mixture and mix well to form a mixture of 8I+lI+IφX8mm.
Manufacture a tablet with an inner diameter of 40 mm and a height of 15 mm.
A reduction test was conducted by raising the temperature in a graphite melting pot at zero temperature. As a result, when heated to 1700°C or higher, silicon carbide was obtained relatively quickly, and silicon carbide was obtained with a yield rate of 9.90% or higher, but below 1650°C, the reaction rate was slow.

Based on this result, we considered continuous production.

Inner diameter 50mφ, 100mφ, 200mmφ, 300-φ
A combustion furnace was constructed using high alumina bricks around the refractory pipe with a length of 2 m, and the above-mentioned tablets were continuously lowered into the refractory pipe. Make a furnace, here diameter 2IIl+ and 4
m pele j) also ij 8 +m.

Cylindrical tablets of 16 cm, 32 cm, 48 cm, and 64 cm (both height and diameter) were produced and charged in the same manner as described above.

211III and 4m were made into pellets because it was somewhat difficult to produce them as tablets.

Initially, 8 mm cylindrical tablets were placed in a refractory tube with an inner diameter of 50 mm, and heated from the bottom with ordinary gaseous fuel or liquid fuel. When burning simply by using air, it is difficult to maintain the temperature above 1700℃;
Maintaining this temperature by enriching the combustion air with oxygen or by preheating it is difficult and unavoidable. Nevertheless, simply carrying out such a reduction caused many problems.

That is, if the temperature of the combustion chamber is maintained at 1,700 to 2,000° C. at the highest point, the fuel efficiency will be extremely poor and the temperature of the exhaust gas in the combustion chamber will also be extremely high. In addition, high oxygen enrichment with a theoretical combustion temperature exceeding 2,500°C will cause uneven heat in the basin, leading to damage to the refractory protection tube, and uneven or sudden reactions of the contents. This results in a decrease in silicon carbide collection. Ultimately, this problem comes down to the fact that carbon reduction in silica stone requires a large amount of reaction heat, and it is difficult to find a way to supply that heat.

For this reason, it is necessary to control combustion at 1,700℃ to 2,000℃.To avoid long flames, gaseous fuels such as hydrogen and carbon oxide are used, and the combustion air is also divided into wide sections in multiple stages. It will be provided by By doing this, we were able to obtain the same product as in a single experiment within the graphite melt.

Next, a combination test of tablets of various sizes and refractory pipes of various sizes was conducted.

The entire pellet with a diameter of 2fi solidified and the efficiency decreased, and the pellet charged in the center of the refractory pipe remained unreacted.

The same result was obtained for 4M tablets.In both cases, the moving layer sometimes causes blow-through and blow-up, and the pressure inside the refractory pipe increases significantly.The product quality of the 8■ tablet is good, but there is some blow-through. Tend.

Since spherical pellets are thought to have better air permeability than cylindrical tablets, this seems to be a size issue rather than a difference in the briquetting method. To prevent this trend, production rates had to be significantly reduced. Based on the above results, we take an intermediate method and estimate that the lower limit size is possible with 6 dimensions and good with 12 dimensions.

The reaction of No. 64 tablets was not completed even though the tablets were lowered down a 2 m high refractory pipe over a period of 3 hours.

For briquettes (-!?lets or briquettes) with a diameter of 8 to 48, D/d where the briquette diameter is d1 and the large pipe diameter is D.
In the range of 5 to 18, if d was the same, the productivity increased in proportion to D2, and the product was good. If it is less than 3.2, the quality of the product will not change, but it will be disadvantageous in terms of production capacity. If it is 25 or more, the unreacted area in the center of the refractory pipe increases, which is not preferable.

However, this tendency was considerably alleviated by passing carbon monoxide gas or alcohol gas through the lower part of the refractory pipe, and the problem was reduced even when the fire rate was 25 times larger. Moreover, when the refractory pipe diameter was 300 mm, an unreacted part remained in the center regardless of the briquette diameter. It was found that this tendency was also alleviated by injecting soot from the lower part of the refractory pipe.

Even if a dense material is used as a refractory, some seepage inside and outside cannot be avoided. Therefore, in order to maintain a completely reducing atmosphere inside the cylinder, it is necessary to inject inert gas from below, while increasing the pressure inside the cylinder to prevent outside oxidizing gas from diffusing into the cylinder. .

A further problem is that if D/d is constant, the production efficiency per unit per hour will almost fall within a constant range as long as the height of the refractory pipe is constant.

To summarize the above, the diameter of the briquette is the most important, and if it is too small or too thick, the quality will deteriorate and the production efficiency will drop significantly.As long as the height of the refractory pipe is constant, the production efficiency of one pipe There is a limit.

Although the diameter of the briquette is based on the results of limited experiments, it is estimated to be between 6 and 56 mins thick. Also, the optimal size is 12-4
Estimated to be 8fi. Although a sphere or cylinder was used in the experiment,
Since the thickness is considered to control heat transfer, it is expressed by the minimum method or thickness of the briquette.

Refractory pipes that can be used here include alumina,
Limited to mullite. The conventionally manufactured products are 1
9 (l) Although it is heat resistant up to 0°C, the length is inevitably limited in order to provide such a structure with mechanical strength.Also, as a dense and non-porous porcelain tube, a length of 1 to 2 m is required. This is the length that is normally produced.In the following example, several tubes were connected together via a joint tube, but as an industrial production furnace, a single tube would have a small and limited capacity. It is necessary to arrange a large number of them in consideration of heat transfer performance.

As is known from the above process, a gaseous fuel that does not undergo incomplete combustion is preferable as a fuel. Therefore, it is preferable to use a gas containing carbon monoxide or hydrogen as a main component. Those containing large amounts of propane, butane, etc. are not preferred. However, as shown in Example 1, it is possible to use nearly half of the required amount of oxygen through partial combustion in the pre-combustion furnace, so there is no problem with the inclusion of a small amount of hydrocarbons.

As the silicic acid raw material, in addition to silicate minerals such as silica stone and silica sand, it is also possible to use compounds and mixtures with oxides of alumina and the like, such as waxite. In this case, a mixture of silicon carbide and other oxides is obtained as a finished product. Petroleum coke, coke, charcoal, etc. can all be used as carbonization raw materials.

The carbon content relative to the silicic acid content in the raw materials is blended at a ratio of 1 mole to 3 moles. When the silicic acid content is higher than this blending ratio, silicon monoxide StO, which is an intermediate product, is scattered as a gas, resulting in a decrease in silicon carbide yield.

- When the blended amount of carbon is large, the excess remains as it is. This carbon content can be removed by oxidation by reheating the product to 800° C. or lower, but generally the carbon content should be added in excess of 5 parts or less of the theoretical amount. Unless the carbon content is blended in a slightly excessive amount, loss as 9 SiO will occur.

Figures 1 and 2 show a pilot plant constructed based on the results of basic tests, and is composed of six highly refractory refractory pipes. Figure 1 is a vertical sectional view of this A
A horizontal sectional view taken along section A is shown in Figure 2.
The cross-sectional view of FIG. 1 is taken along line BB. Reference numeral 1 indicates a raw material briquette 4, and the briquette is kept airtight through a feeder 2, and is supplied to the exhaust gas through a feeder 3 to a refractory pipe 5. The soil is a combustion chamber in which a number of refractory pipes 5, for example six refractory pipes in this example, are constructed and arranged in consideration of the inlets for fuel gas and combustion air or oxygen. 7 is a furnace refractory. The refractory pipe 5 is supported by a support plate 9, but since it is impossible to make intimate contact with the furnace refractory, seals 6 and 8 are made of a low melting point metal such as lead or tin.
Constructed airtight to the end of the combustion chamber. The generated silicon carbide is taken out by a feeder 11 and taken out from a hook 12 to the outside. An inert gas or a reducing gas, preferably carbon monoxide, is introduced into the discharge chamber 10 through a gas inlet 16, thereby preventing the discharge chamber 10 from being overheated by the product. From this point of view, as described in the configuration of the invention, a configuration may be adopted in which the inert gas is actively poured into the refractory pipe 5 in a small amount.

Reference numeral 13 denotes an inlet for combustion support air or oxygen, which is divided into very wide portions and supplied as is clear from the figure. 1
4 is the pile pipe. 15 is a gaseous fuel inlet, 17 is an inlet for combustion support air or oxygen, 18 is an outlet for carbon monoxide produced as a by-product of reduction, and 19 is an outlet for combustion exhaust gas.

In order to make the refractory pipe of sufficient length, short pipes of the same quality can be used and joined as shown. In this case, the material of the upper part, which is at a slightly lower temperature, can be changed to a material with low fire resistance but high spalling resistance and mechanical strength. It is preferable to insert a control valve into the pipe line after the discharge port 18 to increase the pressure inside the refractory pipe 5 higher than the pressure inside the combustion furnace 4.

This can prevent the permeability of the pipe itself and leakage from the pipe joint.

〔Example〕

Next, examples of the present invention will be shown.

[Example 1] The aforementioned pilot plant has an outer diameter of 100 m and an inner diameter of 50 m.
It is made up of six 4m long tubes made of high-purity alumina tubes. Here, a tapelet of 16 mφ x 16 m consisting of silica stone and petroleum coke as shown in the text was supplied. Coke is gasified with a mixed gas of pure oxygen and water vapor to obtain a gaseous fuel containing approximately 33% hydrogen and 654% carbon oxide, which is previously dust-removed and purified. This gas is partially combusted with pure oxygen in a pre-combustion furnace to a temperature of 1500° C., and is introduced from the gaseous fuel inlet 15. Pure oxygen is introduced from the inlet 17, and the furnace is controlled and operated so that the temperature of the twisted zone furnace or refractory pipe with the inlet 13 is 1700 to 190°C as measured by a radiation thermometer.
3. Pour silicon carbide from below into one refractory pipe for 1 hour.
It was obtained at a rate of 5 kg. The collected vehicle is approximately 92 to 95 inches and is a greenish white powder containing several grains of carbon.The gaseous fuel consumption in the entire furnace is 80.4Nms/h, and the use of pure oxygen in the pre-combustion furnace. Amount a: 18.0 Nm"/h, pure oxygen consumption in this combustion furnace: 22.2 Nm"/h
Met.

[Example 2] Exactly the same operation as in the previous example was carried out, except that oxygen was
．． Enriched air enriched with 396% was introduced from the inlet 17. Similarly, if one refractory pipe produces 93.5 k& of silicon carbide per hour, the amount of gaseous fuel gas used is 1
0.7.4 Nm"/h, and the total amount of pure oxygen used to enrich the combustion air with oxygen was 25.8 Nm"/h. The oxygen concentration of the bti combustion support gas may be lowered as long as the temperature can be maintained at 0.degree. C., but the cost of fuel and pure oxygen used will only increase slightly. However, the temperature of the exhaust gas from the exhaust gas outlet 19 rises, and complete combustion produces nitrogen oxides, which must be removed to prevent pollution. Generally, a method with a higher oxygen concentration is preferable. The present invention basically provides a method for producing silicon carbide which has useful applications in addition to conventional gaseous fuels. This silicon carbide is β-type silicon carbide, which is different from those currently used in abrasives, abrasives, and refractory materials. Furthermore, the purity is not always sufficient.

However, by providing silicon carbide at low cost through a simple manufacturing method, the possibility of its use in fields different from conventional ones, such as heating of steel, deoxidizing material, or raw material for ferroalloys, has increased. Of course, it can also be applied to conventional fields. Although it cannot be used as an abrasive, it can be used as a raw material for refractories.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of the reduction furnace used in the present invention, where Figure 1 is a vertical cross-sectional view taken along line BB in Figure 2, and Figure 2 is a cross-sectional plan view taken along line AA in Figure 1. . 1... Hopper, 2... Feeder, 3... Exhaust gas header, 4... Combustion chamber, 5... Refractory pipe, 6...
Seal, 7... Furnace refractory, 8... Seal, 9...
Support plate, 10... Discharge chamber, 11... Feeder, 12
...hopper, 13...inlet, 14...pillar pipe, 1
5... Gaseous fuel inlet, 16... Gas inlet, 17
...Inlet, 18... - Carbon oxide outlet, 19...
- Combustion exhaust gas outlet. Figure 1 Figure 2

Claims (1)

[Claims] A large number of high heat resistant refractory pipes are constructed in the refractory heating chamber,
Gaseous fuel gas is passed through this heating chamber, and air or oxygen-enriched or preheated air is used to burn the gas in stages to form a wide high-temperature zone of 1650 to 2000°C, while inside the refractory pipe from above. A moving packed bed is formed by charging a briquette made by mixing a raw material containing silicic acid with a required amount of reducing carbon, and the reaction product is taken out from the bottom.
! i- A method for producing a silicon carbide or a mixture containing silicon carbide.